1. Field of the Invention
The present invention relates to a vibrator for vibrating gas for generating a jet of the gas, a jet generating device including the vibrator, and an electronic apparatus including the jet generating device.
2. Description of the Related Art
An increase in the scale and speed of large scale integrated circuits (LSI circuits) in recent years have caused electrical power consumption of the LSI circuits to increase year after year. Since most of the electrical power consumed by the LSI circuits is converted into heat energy, the increase in electrical power consumption has led to an increase in the heat value of the LSI circuits. With regard to a system using such an LSI circuit having high electrical power consumption, effort is being made to increase performance of a heat-dissipating system so that the temperature of the LSI circuit does not exceed its maximum operating temperature.
The most general index indicating the performance of a heat-dissipating system is heat resistance. When the temperature of a heat source whose heat value is P[W] is T (° C. or K) as a result of being cooled by a certain heat-dissipating system, a heat resistance Rth[K/W] of the heat-dissipating system is expressed by the following formula:Rth=(T−Ta)/P Here, Ta is ambient temperature (outside air temperature) when is an air-cooling system is used. In order not to increase the temperature of the heat source even if the heat value is high, the heat resistance of the heat-dissipating system is made small. In other words, a heat-dissipating system providing good performance is one having a small heat resistance. For example, in order for a maximum heat value to maintain the temperature of a 20[W] LSI circuit equal to or less than 70° C., under an environment in which the outside air temperature has a maximum value of 40° C., a heat-dissipating system having a heat resistance of less than 1.5 [K/W] is used. When the heat value of the LSI circuit is increased to 100 [W], a typical heat resistance is less than 0.3 [K/W].
A heat-dissipating system which makes use of forceful air cooling basically includes a heat exchanger exchanging heat between a heat source and outside air and an air blower which sends the outside air to the heat exchanger. The heat resistance of this heat-dissipating system may be reduced by increasing efficiency of the heat exchanger or by increasing an air discharge amount of the air blower. For example, by putting thought in the material and structure of a radiating fin or by increasing the surface area of the radiating fin, the efficiency of the heat exchange can be increased. In a system using an axial fan which rotates as the air blower, the air discharge amount can be increased by, for example, increasing the rotational speed or diameter of the fan.
However, in forceful convection of air with such a fan, a temperature boundary layer at a surface of the fin is produced at a downstream side of the fin, thereby giving rise to the problem that heat from the radiating fin is not efficiently removed. This problem may be solved by, for example, reducing the thickness of the temperature boundary layer as a result of increasing fan air velocity. However, increasing the rotational speed of the fan for the purpose of increasing the fan air velocity causes noise to be generated, such as noise from a fan bearing or noise of the wind produced by the fan.
Methods using a vibrating plate that reciprocates periodically (refer to, for example, Japanese Unexamined Patent Application Publication Nos. 2000-223871 (FIG. 2), 2000-114760 (FIG. 1), 2-213200 (FIG. 1), and 3-116961 (FIGS. 3 and 11)) are available as methods which efficiently allow heat from a radiating fin to escape to outside air by destroying the temperature boundary layer without using a fan as an air blower. Of devices in these four documents, in particular, the devices in Japanese Unexamined Patent Application Publication Nos. 2-213200 and 3-116961 include a vibrating plate which roughly divides space in a chamber in two, a resilient member disposed in the chamber and supporting the vibrating plate, and a unit which vibrates the vibrating plate. In these devices, for example, when the vibrating plate is displaced upwards, the volume of an upper space of the chamber is reduced. Therefore, the pressure in the upper space is increased. Since the upper space is connected to the outside air through a suction-exhaust opening, a portion of the air in the upper space is discharged to the outside air by the pressure increase in the upper space. At this time, the volume of a lower space that is opposite to the upper space (the vibrating plate is disposed between the lower space and the upper space) is increased, causing the pressure in the lower space to decrease. Since the lower space is connected to the outside air through a suction-exhaust opening, the pressure reduction in the lower space causes a portion of the outside air existing near the suction-exhaust opening to be sucked into the lower space. In contrast, when the vibrating plate is displaced downwards, the volume of the upper space of the chamber is increased. Therefore, the pressure in the upper space is decreased. Since the upper space is connected to the outside air through the suction-exhaust opening, the pressure reduction in the upper space causes a portion of the outside air existing near the suction-exhaust opening to be sucked into the upper space. At this time, the volume of the lower space that is opposite to the upper space (the vibrating plate is disposed between the lower space and the upper space as mentioned above) is decreased, causing the pressure in the lower space to increase. The pressure increase in the lower space causes a portion of the air in the lower space to be discharged to the outside air. The vibrating plate is driven by, for example, an electromagnetic driving method. Accordingly, by reciprocating the vibrating plate, the discharging of the air in the chamber to the outside air and the sucking of the outside air into the chamber are periodically repeated. Pulsating air induced by a periodic reciprocating movement of the vibrating plate is blown against a heating element such as the radiating fin, so that the temperature boundary layer at the surface of the radiating fin is efficiently broken, as a result of which the radiating fin is cooled with high efficiency.